Given that,
`E_(Zn^(2+)|Zn)^(@)=-0.76V, E_(Cu^(2+)|Cu)^(@)=+0.34V`,
`E_(Ni^(2+)|Ni)^(@)=-0.25V and E_(Ag^(+)|Ag)^(@)=+0.80V`
Which metal ions are reduced by `Ni`?

Explanation

Under standard conditions a metal with a small value of standard reduction potential is a strong reducing agent, and the metal ion of a metal with a large value of standard reduction potential is a strong oxidising agent. The increasing order of the standard reduction potentials of the given half - cells is `E_(Zn^(2+)|Zn)^(@) lt E_(Ni^(2+)|Ni)^(@) le E_(Ag^(+)|Ag)^(@)`. This order indicates that in the given half - cells metals involved have the reducing strengths in the order of `Zn gt Ni gt Cu gt Au`, and the metal ions involved have the oxidising strengths in the order of `Ag^(+) gt Cu^(2+) gt Ni^(2+) gt Zn^(2+)`. Thus, Zn in the strongest reducing metal, and Ag is the weakest reducing metal. On the otherhand, `Ag^(+)` ion is the strongest oxidisng metal ion, and `Zn^(2+)` ion is the weakest oxidising ion.
As Ni is stronger as a reducting agent than either Cu or Ag, it can reduce both `Cu^(2+) and Ag^(+)` ions.